An Evaluation of Objective Measurements of Luster in Suri Alpaca Fleeces and Comparison with Subjective Assessments

Principal investigators:

Angus McColl and Christopher Lupton, PhD
Yocom-McColl Testing Laboratory and Texas A and M University System
San Angelo, TX

100 Suri alpaca samples will be assembled by members of the Suri Network. White, black and 8 standard ARI colors will be equally represented. The full range of luster values and a wide range of fiber diameters will be represented within each color range. Every effort will be made to use samples that are geographically and genetically diverse. The samples will be assessed for color and luster before and after washing by 5 fiber judges and two instruments, the Samba and a near-infrared reflectance spectrometer. In addition, each sample will be analyzed for lab scoured yield, fiber diameter, fiber curvature, and staple length and strength. Using data from the Samba instrument, an estimate of luster will be calculated that is independent of color. Subsequently, mathematical relationships between the Samba and NIRS luster measurements versus subjective luster assessments, lab scoured yield, average fiber diameter (and variability), average fiber curvature (and variability), staple length (and variability) and strength (and variability) will be determined.

The Suri luster study has been published in Small Ruminant Research, the August issue: Lupton, CJ & McColl, A, 2011, Measurement of luster in Suri alpaca fiber, Small Rum Res 99, 178-186.

Lay Abstract

A study was conducted to evaluate the ability of two instruments for measuring luster in Suri alpaca fiber and to compare the results with subjectively assessed luster scores. In addition, the study was designed to determine the correlations between luster and other value-determining, objectively measured physical properties of Suri alpaca fiber. For this purpose, 205 Suri alpaca fleece samples were submitted by 49 breeders that represented a broad cross-section of Suri alpaca in terms of visually assessed luster, color, and fiber characteristics. Raw staples and “washed-and-aligned” staples were independently and subjectively assessed for luster by 2 alpaca judges certified by the Alpaca Owners and Breeders Association (AOBA). The fiber samples were measured for luster and luminance (a measure of color) using a SAMBA Hair System and were scanned using a near-infrared reflectance spectrometer. Standard objective test methods were used to measure mean fiber diameter and variability (at mid-staple and overall), prickle factor, comfort factor, mean fiber curvature and variability, medullation (white, beige, and light fawn samples only), laboratory scoured yield, mean staple length and variability, and mean staple strength and variability. The precision of the luster measurement (MLUS) was estimated using the coefficient of variation (CV) statistic based on 3 measurements per subsample and averaged 3.9% across all colors. In contrast, precision of the luminance measurement (MLUM) was higher with an average CV of 2.3%. Agreement between the subjective luster scores of 2 certified alpaca judges was low (r2 = 0.17 and 0.10 for raw and washed-and-aligned samples, respectively). Despite this, evidence was obtained linking instrument-measured luster and luminance with subjectively assessed luster scores. Two systems were proposed for expressing SAMBA instrument-measured luster that will permit comparisons between alpacas of different color. Small negative correlations were present between mean fiber diameter and subjectively assessed luster scores. Small positive correlations were present between mean fiber diameter and objectively measured luster values. A strong correlation (r = -0.94) existed between instrument-measured luster and log10luminance. Prediction equations derived from near-infrared reflectance spectra (NIRS) produced precise and accurate estimates of log10luminance. The NIRS estimates of instrument-measured luster were less precise and less accurate, and estimates of subjectively assessed luster were neither accurate nor precise. The SAMBA Hair System is capable of producing estimates of luster that are accurate enough to be useful to Suri alpaca breeders who intend to select for this trait.

Keywords: Alpaca; Suri; Luster; Objective fiber measurements; Near-infrared reflectance spectrometer.

Acknowledgements

The authors wish to express their appreciation to the Alpaca Research Foundation and the Suri Network for financial support of this project and to the cooperating breeders who shared in the cost of the testing.

Additional information

A refereed journal article resulting from this study is available on line on the Small Ruminant Research web page. It is expected to be available in hard copy in the June or July edition of the journal.